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What’s in an orange?

Oranges are a rich source of bio-based chemicals. Dr Avtar Matharu from the Green Chemistry Centre of Excellence explains what's in an orange.
Our planet today is under severe stress. We are consuming too much and generating too much waste. Earth has a population of 7.5 billion people, and this is predicted to increase to around 10 billion by 2050. How do we provide all the things 10 billion people need like clean water, sanitation, health care, food and nutrition? All these challenges and more have been identified by the United Nations under the banner of 17 Sustainable Development Goals. Within those challenges we have the 5 Ps - Planet, People, Prosperity, Partnerships and Peace. All of these are interconnected and they affect us all. The area of research I work on is what’s known as unavoidable food waste.
When you peel an orange you’re generating unavoidable food waste and throwing part of the product, which you’ve paid for, away. That does not make good business, environmental or social sense. When you peel an orange you will notice the distinctive smell of orange on your hands. That smell is orange essence, or limonene. Limonene is a scent used by the perfume and fragrance industry but also it’s a fantastic household cleaner. Limonene can be extracted from orange peel using microwave technology. Limonene can also be used to help solve the problem of polystyrene waste. Limonene likes to dissolve things and can be used as a solvent to dissolve polystyrene, reducing it into a concentrated solution.
This is already happening in Japan, where lorries containing orange oil collect polystyrene waste from offices for concentration. On the inside of the orange peel, we have the pith and from this we can extract pectin. Pectin is used widely in food production, such as in jam making and as a viscosity modifier. Pectin can be used to thicken and provide mouth-feel for low fat products, such as mayonnaise. Ideally a lot of the materials that we recover from unavoidable food waste should be used in this way, that is, for nutritional purposes again. When the limonene and pectin have been removed from orange peel, the material left over can be further processed into a powder called microfibrillated cellulose or MFC.
MFC can be used to make hydrogels - materials that trap water, and thus, can also be used in food and medical industries. So, in conclusion, there’s a lot more in an orange than just fruit or its juice. Unavoidable food wastes, such as orange peel, offer real value, opportunity and solutions to tackle global grand challenges, resource efficiency and lead to a sustainable, circular economy.

We all know that oranges are good to eat, but have you ever given any thought to the peel that you discard after eating one?

There’s often a lot of value that can be extracted from unavoidable food waste, like orange peels. In this video Dr Avtar Matharu explores the valuable materials that can be found in orange peel and discusses their potential applications.

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Bioeconomy: How Renewable Resources Can Help the Future of Our Planet

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